diff --git a/unix/gtkdlg.c b/unix/gtkdlg.c
index 67d0786a..0cb8b7e0 100644
--- a/unix/gtkdlg.c
+++ b/unix/gtkdlg.c
@@ -3960,7 +3960,7 @@ void showeventlog(void *estuff, void *parentwin)
     c->listbox.percentages[2] = 65;
 
     es->window = window = our_dialog_new();
-    title = dupcat(appname, " Event Log", NULL);
+    title = dupcat(appname, " Event Log", (const char *)NULL);
     gtk_window_set_title(GTK_WINDOW(window), title);
     sfree(title);
     w0 = layout_ctrls(&es->dp, &es->scs, s0, GTK_WINDOW(window));
diff --git a/windows/windlg.c b/windows/windlg.c
index 94e5ad93..352ae1fc 100644
--- a/windows/windlg.c
+++ b/windows/windlg.c
@@ -779,7 +779,7 @@ void logevent(void *frontend, const char *string)
 
     if (*location)
         sfree(*location);
-    *location = dupcat(timebuf, string, NULL);
+    *location = dupcat(timebuf, string, (const char *)NULL);
     if (logbox) {
 	int count;
 	SendDlgItemMessage(logbox, IDN_LIST, LB_ADDSTRING,